Re: Pedagogy

[Hugh Logan <HloganPHY@CFL.RR.COM>]

Hugh Haskell wrote:

> I found, quite by accident, that if I clearly didn't know how to
> solve a problem once it was raised, and the students got to watch my
> thought processes as I worked through it, it helped them. Once I
> stumbled on to this, I would try to get a problem or two tossed out
> each week that I didn't know how to solve before-hand, and then as I
> worked through the problem, I would point out explicitly what I was
> doing and why. If I had to flail a bit to find a method, I pointed
> that out. If I was trying a couple of different approaches to see
> which one worked, or worked better, they were told that, too.

I recall reading about this approach over thirty years ago in a little
paperback about education by a cognitive psychologist -- probably by
Jerome Bruner. My copy is packed away, so I can't refer to it now. The
author suggested presenting the students with a problem that one can't
solve himself. This can work, but there is always the risk of the
student asking, "If you can't do it, how do you expect us to do it?"
I think that in very conservative schools, the teacher is expected to be
the authority.

Back in the late 1980's, we had a small engineering physics program at
the technology college where I taught. I was involved with a laser
optics course, which had to include all the optics the students needed
-- geometrical and physical. I resucitated an old Fabry-Perot
interferometer, and was able to use it successfully. On my own, I
decided to use it to see if I could use it to demontrate the Zeeman
effect using a mercury light source. I had done the experiment in the
advanced lab at Cornell Summer School in 1970 -- using a Lummer-Ghercke
plate if I remember correctly. At Cornell, students worked individually,
but, at least, one was quite sure that the ancient, but well-kept,
equipment would work. They undoubtedly used a mercury source designed
for this type of experiment. I was unable to detect any Zeeman splitting
of the lines. We had a nice mercury source, but not designed for this
purpose. We could not afford to buy much specialized equipment or a
ready-made Zeeman setup. The electromagnet had a maximum field not as
great as the one I used at Cornell -- about half as great -- but it
should have been strong enough to demonstrate the effect according to my
old lab notebook. I saw no splitting. That summer, another teacher and
his students decided to do the experiment in an experimental physics
course. The assumption was that the magnetic field wasn't strong enough.
It was left more or less as a research project. One student decided to
unwind the magnet, rewinding it with thin copper tubing through which
oil was circulated as a coolant, hoping to be able to use a much larger
current. Of course, the number of turns was reduced, so it would have
taken a huge current to produce the field they wanted. When they tried,
the apparatus exploded, the students narrowly escaping injury from the
hot oil -- as one of them told me. I was glad I was not involved. The
expensive magnet was useless, and another teacher insisted that the
school buy another one, which they did -- this time a larger one costing
quite a few thousand dollars. I was assigned the laboratory course the
following summer. We tried to do the Zeeman effect again, using the new
and bigger magnet. Still no observed Zeeman splitting. I didn't have an
answer. We were still using the same mercury source. One of the students
got the idea of using an ordinary mercury spectrum tube, although I am
not sure why he thought of this. The Zeeman splitting was observed on
the first attempt. It immediately occurred to me that the reason that we
did not observe the Zeeman effect with the first mercury tube was
because of pressure broadening, the original tube being at higher
pressure. The original magnet would undoubtedly have been sufficient.
This is my most vivid experience of learning by discovery with a problem
that we , at first, could not solve -- albeit a very expensive discovery.

Hugh Logan,
Retired physics teacher